There are a number of prior art automatic air brake systems, one of which is disclosed in NABUKO GIHOO, No. 63, published on Jan. 1, 1987. An exemplified embodiment of a prior art system is illustrated in FIG. 7 of the drawings, and will be presently explained in the specification of the subject application.
In viewing FIG. 7, it will be appreciated that the system is shown in a brake released condition.
At this time, the brake valve BV3 is moved to the running position and a balance discharge valve inside the valve is in a closed position. Thus, the balance air reservoir ER and the pilot chamber A of the relay valve RV3 are pressurized to a specific pressure level and are maintained at the specified pressure, such as, 5 Kg/cm.sup.2.
In addition, the controller CB3 switches the electromagnetic valve MV3 to an OFF condition since the status signal S from the brake valve BV3 is equal to zero (0). Therefore, the electromagnetic valve MV3 is in a first exhaust position .tau. so that the expansion air reservoir BR is opened to the atmosphere.
Further, the relay valve RV3 assumes a lapped position in which the pressure pilot chamber A is maintained at a specified pressure so that the output chamber B and the brake line BP are maintained at a specified pressure, and the air supply valve D is seated on the hollow exhaust valve rod C and is also seated on the air supply valve seat E. Thus, the output chamber B is closed off from the air supply chamber F and the exhaust chamber G. Thus, the forces pushing on the balance piston H from the up and down directions, as shown in FIG. 7, are balanced or equalized.
Since the pressure in the brake line BP is maintained at a specified pressure by the brake valve BV3 and the relay valve RV3, the brake control valve CV of the lead unit or locomotive and the pressure of the brake control valves of the following freight cars are exhausting. However, the pressure in the supplemental air reservoir AR is maintained at a certain pressure, and the brake cylinder BC is opened to the atmosphere via the exhausting hole Ex. The brake control vale CV may be a conventional two-pressure type of control valve or a conventional three-pressure type of control valve and, therefore, detailed explanations are omitted for the sake of convenience.
In the normal running mode, as shown in FIG. 7, the brake valve BV3 is placed into the normal brake position so that the balance air reservoir ER is exhausted by the brake valve BV3. The balance discharge valve (not shown) in the brake valve BV3 opens and exhausts the brake line BP to atmosphere. Simultaneously, the relay valve RV3 exhausts the brake line BP to atmosphere.
During this normal brake action, the pressure in the balance air reservoir ER is higher than a predetermined pressure, e.g., 4.8 Kg/cm.sup.2, and also the condition signal S from the brake valve BV3 switches to a position in which is equal to S=1 so that the commander CB3 switches the electromagnetic valve MV3 to the ON condition, namely, the second position .quadrature..
Therefore, the compressed air in the balance air reservoir ER flows into the expansion air reservoir BR. Thus, the balance air reservoir ER is partly exhausted in the early stage of normal braking so that the balance discharge valve (not shown) in the brake valve BV3 and the balance piston H of the relay valve RV3 definitely start to operate early and the exhaustion of the brake line BP begins early.
When the pressure in the balance air reservoir ER becomes lower than the above-mentioned predetermined pressure, namely, 4.8 Kg/m.sup.2, the controller CB3 switches the electromagnetic valve MV3 to its OFF position so that it returns to the first position .tau.. However, the balance air reservoir ER is still being continuously exhausted by the brake valve BV3.
Accompanying this exhaustion of the balance air reservoir ER, the pilot chamber A of the relay valve RV3 is also exhausted so that the force pushing the balance piston H upward becomes smaller than the force pushing it downward so that the balance piston H moves downwardly. Thus, the exhaust valve rod C, which is part of the piston, moves downward and unseats from the air supply valve D. Accordingly, the brake line BP is open to the atmosphere via output chamber B, exhaust valve rod C, and through exhaust chamber G. This is called exhaust operation.
Because of this exhaustion of the brake line BP, the brake control valve CV in each railway car initiates an air supply action and causes the closure of exhaust opening EX. At the same time, air is supplied from the supplemental air reservoir AR to the brake cylinder BC.
After the balance air reservoir ER is exhausted a certain amount by the brake valve BV3, the brake valve BV3 is moved into the lap position (not shown). Thus, the exhaustion by the internal balance discharge valve ceases and the balance air reservoir ER maintains the existing pressure at the time. Simultaneously, the relay valve RV3 returns to the lap state, as shown in FIG. 7. Thus, the brake line maintains the existing pressure at that time, and each railway car maintains the braking operation at that time. During this time, the status signal S is equal to zero (0).
In this brake maintenance state, if the brake valve BV3 is moved into the running released position, the balance air reservoir ER is pressurized to a certain pressure. Accompanying this, the pilot chamber A of the relay valve RV3 is pressurized so that the balance piston H and the exhaust valve rod C are moved upwardly. This causes the air supply valve D to be unseated from the air supply valve seat E, and the air is supplied from the original air reservoir line MRP to the brake line BP through the air supply chamber F and the output chamber B. This is called the air supply operation. When the force pushing the balance piston downwardly increases by the pressurization of the output chamber B, and when the output chamber B reaches a certain pressure, the relay valve RV3 returns to the lap state or position, as shown in FIG. 7.
In the above-described embodiment of the prior art arrangement, if the train is long, i.e., if a great number of cars are connected to the train, the exhaustion from the locomotive by the brake line BP is unduly delayed due to the slow speed of the transmission of the air caused by the resistance in the brake line BP. Thus, the exhaustion state of the brake line BP in the last railway car of the train is delayed in comparison with that of the locomotive. When the brake line BP in the locomotive has already reached a predetermined exhaustion, the brake line of the last car is not yet exhausted to that amount. It will be seen that the brake valve BV3 and the relay valve RV3 impede the exhaust capacity. Consequently, the exhaustion of the brake line BP of the last car is delayed even further.
In other words, when the brake line valve BV3 is in the normal brake position, the balance air reservoir ER is being exhausted. Thus, a pressure difference is generated between the brake line BP and the balance air reservoir ER. Because of this pressure difference, the balance discharge valve of the brake valve BV3 and the exhaust valve rod C of the relay valve RV3 becomes fully open and result in a large exhaust capacity. Then, when the brake valve BV3 is put in the lap position, the exhaustion of the balance air reservoir ER stops, and the pressure difference in the brake line BP of the locomotive and the balance air reservoir ER becomes smaller. Thus, the balance discharge valve and the exhaust valve rod C shift to the lap direction so that the exhaust capacity gradually becomes smaller. However, the brake line BP of the last car has not yet reached the specified point of exhaustion.
As explained above, despite the fact that the brake line BP of the car is still being exhausted, the brake line BP of the leading locomotive approaches a specified exhaustion and restricts the exhaust capacity. However, the large exhaust capacity cannot be maintained until the brake line BP of all of the cars is exhausted by a certain amount.
Therefore, in practicing this invention, the brake line of the locomotive is exhausted more than a specified value, that is, it appears to be over-exhausted while the exhaust capacity of the relay valve is kept large until the exhaustion of the brake line of the last railway car reaches a certain value. After that, the above-mentioned over-exhaustion is stopped. The method used in practicing the present invention may be described as follows:
First, a flow detector senses and detects the flow rate of the compressed air in the brake line of the locomotive. The flow detector is constructed so that when a normal braking command is given, the pilot chamber of the relay valve is supplemented by the over-exhaustion to accelerate the exhaustion of the brake line. Now, when the flow signal from the flow detector exceeds a predetermined value, the over-exhaustion is stopped. When the flow signal becomes lower than the predetermined value in an automatic air brake system, the brake lines of the railway cars are pressurized or exhausted by the relay valve of the locomotive.
Generally, in the railway cars of the train, when the normal braking command is given, the brake line of the locomotive is exhausted by a certain amount. However, the pressure in the brake line of the last car will still be relatively high due to the lag in the transmission time. While this pressure difference is large, the air flow in the brake line from the last car to the locomotive is relatively large. Now, as the brake line of the last car reaches a certain level of exhaustion, the pressure difference in the brake line of the locomotive and the last car becomes smaller. Thus, the air flow in the brake line into the locomotive becomes small, and the air flow in the brake line in the locomotive decreases. In this invention, the air flow in the brake line of the locomotive is detected, and an evaluation is made whether to pressurize the pilot chamber of the relay valve to a certain amount or to exhaust it by a specified amount.
First, if the air flow exceeds the predetermined value, in other words the brake line pressure of the last car remains high while the brake line pressure of the locomotive is exhausted by a certain amount, the pilot chamber of the relay valve is over-exhausted and, therefore, the exhaust capacity of the relay value is kept large and the exhaustion of the brake line of the last car is accelerated.
When the above-mentioned air flow becomes lower than a predetermined value, in other words, when the brake line of the last car approaches a specified amount of exhaustion, the over-exhaustion of the above-mentioned pilot chamber is stopped and returns to a specified exhaustion value. After that, it exhausts the brake line of all of the railway cars of the train by a certain amount.
The flow of air in the brake line of the locomotive which controls the above-mentioned over-exhaustion or a specified amount is proportional to the pressure difference in the brake line of the locomotive and the last railway vehicle so that in the case of a short train, the pressure difference is small. Thus, the air flow is small and quickly decreases. Accordingly, the time to over-exhaust the pilot chamber of the relay valve is short. Conversely, in the case of a long train, the pressure difference is large and the air flow is also large so that the pilot chamber of the relay valve remains in an over-exhaustion condition during that time.
In addition, the flow of air in the brake line of the locomotive, is proportional to a specified exhaustion value, namely, a normal brake command value, so that the specified exhaustion value is large. Now, when the exhaustion value becomes small, the specified exhaustion value is small. This corresponds to the flow of air so that the pilot chamber of the relay valve is over-exhausted or exhausted by a certain amount.
Therefore, according to this invention, the pilot chamber of the relay valve is over-exhausted until the brake line of the last car reaches a specified exhaustion value. In this manner, the exhaust capacity of the relay valve can be kept large so that the exhaustion of the brake line of the last car can be quickly accelerated. In addition, it automatically compensates for the difference in the number of railway cars or a specified exhaustion value, namely, normal brake command value. Therefore, it can accommodate each condition with the same type of control pattern so that a normal brake command acceleration effect corresponding to its status can be obtained.